The present invention relates generally to Radio Frequency Identification (RFID) Tags and the methods of producing such tags.
The design of a typical RFID tag reflects its origin in the semiconductor and printed circuit board industries. Although functional, the design has a number of features that increase the cost of the finished article. In a resonant RFID tag, the electrical inductance of an antenna is connected in parallel with a capacitor such that the resonant frequency of the thus-formed circuit is tuned to a prescribed value. In more advanced forms, the circuit of the RFID tag may include an integrated circuit die electrically and mechanically bonded to the antenna on a substrate, wherein the voltage induced in/on the antenna by a reader signal provides power to operate the integrated circuit on the die.
The antenna typically includes a metal coil pattern on one side of a substrate, and metallization on the second side of the substrate to cross over the antenna, i.e., bring the outer connection of the multi-turn antenna coil back to the open unpatterned area in the center, where the die is typically located and bonded. Vias, i.e., electrical connections through the substrate, connect the first side metallization to the second side metallization. Typically one connection is made at the outer perimeter of the antenna to the second side metallization, and a second connection interior to the antenna coil brings the second side metallization in contact with the die bonding pad on the first (coil) side metallization.
The die is bonded between the antenna and second side metallization such that it completes the circuit between the ends of the antenna. The antenna center frequency is often tuned by laser-trimming the area of a capacitor plate formed between the first surface and second surface metallization.
Several problems exist with the current method of manufacturing RFID tags. For example, because metallization is formed on both the front and back sides of the substrate, alignment between the two sides is crucial. Aligning the two sides presents challenges that are difficult to overcome and are costly. In addition, where the front side to back side alignment is not accurate, fabrication yield can be reduced.
The present invention provides folded radio frequency identification (RFID) tag devices and methods for high-volume, low-cost production. The folded construction of the devices and methods of the present invention presents a number of advantages over the prior art. For example, the present invention reduces the complexity of the typical two-sided RFID tag with through-substrate via connections by providing a one-sided circuit design. This obviates the need for through-substrate via connections, while also addressing front side to back side alignment issues.
Another advantage of the devices and methods of the present invention is that the resonant frequency of circuits formed on the RFID tag devices of the present invention may be tuned by severing selected connections to one or more tuning capacitor plates that form a part of the capacitor structure. Severing connections to the tuning capacitor plates changes the capacitance of the circuit which, in turn, changes the resonant frequency of the circuit.
This invention may also reduce the number of connections in the RFID tag. The reduced number of connections may improve initial reliability and manufacturing process yield. In addition, fewer connections may also limit the sites of potential failure due to long-term aging conditions.
Another advantage of the present invention is that the process of folding the substrate can simultaneously form the end-to-end connection for the antenna loop and the capacitor structure. The folding process may be automated if so desired.
The devices and methods of the invention can be used to manufacture RFID tag device that do not include an integrated circuit die for use as Electronic Article Surveillance (EAS) devices. Such devices may be deactivated by methods known in the art, such as exposing the device to a high intensity electromagnetic field at the resonance frequency. The large voltage induced in the circuit on the device may drive a current through any conductive medium used to join the circuit at the connection pads that is large enough to destroy the required electrical interconnection. Alternatively, the large voltage induced in the circuit may cause a conductive channel to form in the dielectric layer of the capacitor, thus destroying or changing the capacitance of the circuit. After deactivation, the device will no longer significantly interact with the electromagnetic field at the operating frequency of the inquiring system. Conversely, if the device is not deactivated, it will interact with a sensing field to indicate that an article is being removed from a controlled area.
In some embodiments of the present invention, an integrated circuit die may be attached to a die connection site that forms a part of the circuit, thus forming an RFID tag device including additional functions or features, e.g., memory, etc. The die connection site may, in some embodiments, include die connection terminals that are made by separating an integrated die connection pad before attaching the die. If desired, the deactivation methods described above may also be used to deactivate RFID tag devices that incorporate an integrated circuit die.
The circuit patterns may be formed on a continuous web that can be separated to provide a number of individual RFID tag devices. The circuit patterns could be complete prior to separation of the web, or the circuit patterns could be partially formed, separated from the web, and then completed. Alternatively, a die could be attached at the die connection site either before or after the web is separated into the individual RFID tag devices.
In one aspect, the present invention provides a method for fabricating a radio frequency identification tag device. The method includes providing a substrate with first and second major surfaces, wherein a first portion of the substrate forms a connector tab. A circuit pattern is provided on a first major surface of a substrate, the circuit pattern including an antenna pattern having first and second ends; a first connection pad and a second connection pad, wherein the first connection pad is located on the first major surface of the substrate within the connector tab. The circuit pattern also includes a common capacitor plate in electrical communication with the antenna pattern; and a plurality of tuning capacitor plates, each of the tuning capacitor plates in electrical communication with the antenna pattern through a tuning capacitor plate connection. The method further includes folding the connector tab along a connector tab fold line such that the first major surface of the substrate within the connector tab faces the first major surface of the substrate outside of the connector tab; wherein the plurality of tuning capacitor plates are located on the connector tab or the common capacitor plate is located on the connector tab such that the plurality of tuning capacitor plates and the common capacitor plate form a capacitor after the folding; and wherein the first connection pad faces the second connection pad after the folding.
In another aspect, the present invention provides a method for fabricating a radio frequency identification tag device on a substrate with first and second major surfaces, wherein a first portion of the substrate forms a connector tab. The method further includes providing a circuit pattern on a first major surface of a substrate. The circuit pattern includes an antenna pattern with first and second ends; a first connection pad and a second connection pad, wherein the first connection pad is located on the first major surface of the substrate Within the connector tab; a common capacitor plate in electrical communication with the antenna pattern; and a plurality of tuning capacitor plates, each of the tuning capacitor plates in electrical communication with the antenna pattern through a tuning capacitor plate connection. The method also includes folding the connector tab along a connector tab fold line such that the first major surface of the substrate within the connector tab faces the first major surface of the substrate outside of the connector tab, wherein the plurality of tuning capacitor plates are located on the connector tab or the common capacitor plate is located on the connector tab such that the plurality of tuning capacitor plates and the common capacitor plate are located opposite each other after the folding, and further wherein the first connection pad faces the second connection pad after the folding. A dielectric layer is located between the common capacitor plate and each of the tuning capacitor plates, wherein the common capacitor plate and the tuning capacitor plates are separated by the dielectric layer after the folding. The first connection pad is placed in electrical communication with the second connection pad; the resonant frequency of the device is measured; and at least one of the tuning capacitor plate connections is selectively severed such that a desired resonant frequency is obtained.
In another aspect, the present invention provides a radio frequency identification tag device that includes a substrate with first and second major surfaces, a first portion of the substrate forming a connector tab, wherein the substrate is folded along a connector tab fold line such that the first major surface of the substrate located within the connector tab faces the first major surface of the substrate outside of the connector tab. The device further includes an antenna located on the first major surface of the substrate; a first connection pad located on the first major surface of the substrate within the connector tab; a second connection pad located on the first major surface of the substrate outside of the connector tab, wherein the first and second connection pads face each other and are in electrical communication with each other. The device further includes a capacitor with a common capacitor plate in electrical communication with the antenna and a plurality of tuning capacitor plates separated from the common capacitor plate by a dielectric layer, each of the plurality of the tuning capacitor plates in electrical communication with the antenna through a tuning capacitor plate connection, wherein only one of the common capacitor plate or the plurality of tuning capacitor plates is located within the connector tab.
In another aspect, the present invention provides a radio frequency identification tag device including a substrate with first and second major surfaces, a first portion of the substrate forming connector tab defined by a connector tab fold line and a separation line formed in the substrate, wherein the substrate is folded along the connector tab fold line such that the first major surface of the substrate located within the connector tab faces the first major surface of the substrate outside of the connector tab. The device also includes an antenna located on the first major surface of the substrate; a first connection pad located on the first major surface of the substrate within the connector tab; and a second connection pad located on the first major surface of the substrate outside of the connector tab, wherein the first and second connection pads face each other and are in electrical communication with each other. Also included in the device is a capacitor having a common capacitor plate in electrical communication with the antenna and a plurality of tuning capacitor plates separated from the common capacitor plate by a dielectric layer, each of the plurality of the tuning capacitor plates in electrical communication with the antenna through a tuning capacitor plate connection, wherein only one of the common capacitor plate or the plurality of tuning capacitor plates is located within the connector tab. The device further includes at least one disconnected tuning capacitor plate located opposite the common capacitor plate and separated from the common capacitor plate by the dielectric layer, wherein the disconnected tuning capacitor plate is not in electrical communication with the antenna.
These and other features and advantages of the invention are described below with respect to illustrative embodiments of the invention.